1. Field of the Invention
The present invention relates to hydraulic couplings used in undersea drilling and production applications and seals used in those couplings. More particularly, the invention involves a three-piece coupling with a radial metal seal for sealing the junction between the male and female members of the coupling.
2. Related Art
Subsea hydraulic couplings are old in the art. The couplings generally consist of a male and a female member with soft seals to seal the junction between male and female members.
The female member is generally a cylindrical body with a relatively large diameter longitudinal bore at one end and a relatively small diameter longitudinal bore at the other. The small bore facilitates connections to hydraulic lines, while the large bore contains the soft seals and receives the male portion of the coupling. The male member includes a cylindrical portion at one end to facilitate connection to hydraulic lines. When the cylindrical portion of the male member is inserted into the large bore of the female member, according to the various embodiments of the device, the soft seals, resembling O-rings, either abut the end, or face, of the male member or engage the male member about its circumference. The hydraulic fluid is then free to flow through the female and male portions of the couplings, and seals prevent that flow from escaping about the joint in the coupling.
In some instances, a check valve may be installed in the female member and also in the male member. Each check valve is open when the coupling is made up; however, each check valve closes when the coupling is broken, so as to prevent fluid from leaking out the system of which the coupling is a part.
The soft seals have numerous disadvantages, the principle ones being (1) the inability of the seal to withstand the deteriorating effects of the subsea environment for extended periods of time, and (2) the inability of the soft seal to contain the higher pressures being imposed on the hydraulic systems.
A metal seal is available which better withstands both the deteriorating effects of the environment and higher pressures. That seal is a crush type which is positioned between the end of the male portion of the coupling and the internal end of the large bore in the female portion. When the male portion is inserted into the female, the metal seal is crushed between the two portions and a seal is effectuated between the two. In view of the crushing action, the seal can be used only once. If the coupling is separated for any reason, the once crushed seal can be replaced with a new seal. An example of this type of coupling and seal is shown in U.S. Pat. No. 3,918,485.
Another type of hydraulic coupler with a metal seal is disclosed in U.S. Pat. No. 4,647,470. As may be seen, this design uses a V-shaped metal seal. The metal V-seal rests in the female member and is only effective when it is tightly compressed by pressure from the leading face of the male member. This means that substantial forces are needed to lock the coupling in the first place and to keep it locked under the necessary pressure. This design could leak even upon slight separation of the male and female coupling members, which is a problem because of the internal pressures when each hydraulic line is pressured up, as discussed above. The V-seal coupling requires a preload mechanism to prevent separation of the coupling members. Extremely close tolerances are required both for the couplings and manifold plates. In principal, the V-seal coupling was reusable and the coupling could be disengaged and reengaged more than once without replacing the seal. In practice, however, the V-seal would quite often flip out or flip sideways when the coupling was disconnected. If the coupling was reconnected without repositioning the V-seal, the coupler would be damaged beyond use.
In U.S. Pat. No. 4,694,859 to Robert E. Smith III, an undersea hydraulic coupling with a radial metal seal is disclosed. This coupling provides a reusable radial metal seal which engages the circumference of the probe when it is positioned within the female member body. The metal seal is held in place by a cylindrical body or retainer. The retainer prevents escape of the metal seal from the female member body. When the male and female portions of the coupling are parted under pressure, the retainer prevents the metal seal from blowing out through the bore of the female member. This coupling uses a pressure actuated C-ring seal. Among the advantages of this design are that it requires no preload mechanism, is tolerant to movement of the two halves of the coupling relative to one another, and allows greater tolerances between the couplings and the manifold plates. Rather than sealing with the leading face of the male member (as done by the V-seal coupling), this design uses a pressure energized C-seal for sealing with the outer circumference of the male member. The retainer also may be used to pre-load the C-seal by urging it radially inwardly to engage the circumference of the male member. This is accomplished by positioning the seal on a shoulder within the female member bore, then locking the retainer against the seal.